Magnetic tool for retrieving metal objects from a well bore

ABSTRACT

A magnetic tool for retrieving metal objects from a wellbore has a plurality of magnet assemblies spaced longitudinally along a tool body. Each magnet assembly has a plurality of magnet members covering a majority surface area of the tool body. Each magnet member has a magnet body and a shield encasing the magnet body and protecting the individual magnet body from striking force created by the attracted metal particles. The shield is preferably made from a non-ferrous material and allows concentration of the magnetic force away from the tool body and into the casing annulus.

BACKGROUND OF THE INVENTION

The present invention relates to wellbore tools and more particularly to a magnetic tool for retrieval of metal objects, such as cuttings and other foreign objects that accumulate in the process of perforating or milling over bridge plugs and other down hole obstructions from a wellbore.

Various types of bridge plugs are conventionally used in the oil and gas industry. These bridge plugs are installed in the annulus and are often covered in cement. Removal of such plugs can sometimes pose a problem for the industry. A rotary bit drills the cement and plugs out, while some of the cuttings of the plugs are carried out to the surface by a liquid circulated down hole.

Sometimes, a production packer needs to be removed together with the metal pipe that it surrounds. In those cases, milling tools with gravity fed boot baskets are used for retrieving pieces of metal from the wellbore. After retrieval of the production packer, it may become necessary to run a conventional fishing magnet to retrieve additional metal debris and cuttings.

A conventional fishing magnet is mounted inside a housing that is lowered into a wellbore. It is limited in the ability to retrieve cuttings in that its magnetization is restricted to the extreme bottom surface of the magnet. The fact that circulating fluids lift the cuttings away from the bottom surface of the magnet renders that conventional fishing magnet useless in this situation. Often times, a boot basket is used for collecting cuttings that did not attach themselves to the conventional magnet. A boot basket has small openings for catching these particles. Consequently, many large size pieces or very small pieces suspended in the fluid flow are not trapped in the basket and remain in the wellbore.

Other magnetic tools utilize magnet assemblies that are secured on a cylindrical body and form a surface for attracting the metal objects located in a well bore. One of such tools is disclosed in U.S. Pat. No. 6,354,386. The apparatus for retrieving metal objects in accordance with the '386 patent discloses a tool having a plurality of magnet assemblies spaced longitudinally along the length of the tool body. Each of said magnet assemblies has a plurality of spaced elongated magnet members. Each magnet member has a magnet protector that extends outwardly from an exterior of the tool body to a distance greater than a corresponding magnet member to protect the corresponding magnet member from striking force of metal particles being attracted by the magnet member, while retaining a distance between the magnet protector and an adjacent magnet member.

While the tool of the '386 patent works quite satisfactory in most conditions, it was observed that some of the metal debris may still strike the magnet surface and have a potential of damaging the magnets. Additionally, the non-ferrous shield, or protector may allow some of the magnetic field to disperse into the tool body instead of concentrating the magnetic force entirely outwardly.

The present invention contemplates elimination of drawbacks associated with the prior art and provision of a wellbore tool for removal of metal objects, such as cuttings, and other foreign particles that provides for the use of sets of magnets spaced longitudinally along the tool body and magnet protectors enveloping individual magnet members.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an apparatus for retrieval of metal cuttings and other foreign objects from a wellbore.

It is another object of the present invention to provide a magnetic tool for retrieving metal objects from a well bore that protects magnet members, while concentrating the magnetic force into the casing annulus.

These and other objects of the invention are achieved through a provision of an apparatus for removal of metal cuttings and other foreign objects from a wellbore that uses at least two magnet assemblies vertically spaced from each other and mounted on the body of the tool. Each magnet assembly is comprised of a plurality of magnets encircling the body of the tool and covering a surface area greater than one half of the tool body.

Each of the magnet members is encased in a protective shield, which has an inner wall of increased thickness and thin outer walls so as allow the magnetic force to be concentrated and directed outwardly from the tool body. The magnet members, as well as the casing may have rectangular or trapezoidal cross-section and be made from a non-ferrous material. Consequently, the capability of the tool to retain cuttings for subsequent retrieval to the surface is significantly increased in comparison with conventional magnet tools.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the drawings, wherein like parts are designated by like numerals and wherein

FIG. 1 is a schematic view showing position of the apparatus of the present invention in combination with a conventional milling tool.

FIG. 2 is a side view of the magnetic tool tool of the present invention.

FIG. 3 is a top view of the magnet tool of the present invention positioned in a casing.

FIG. 4 is a side view of a magnet member; and

FIG. 5 is a detail view of the magnet casing, or protector.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings in more detail, numeral 10 designates the well bore tool in accordance with the present invention. The tool 10 comprises a cylindrical body 12 having a through opening 14 for admitting circulating fluid into a wellbore 34. The cylindrical body 12 carries an upper sub 16, which has external threads 18, and a lower sub 20 provided with internal threads 22. The threads 18 allow connection of the tool 10 to a bumper jar 30 schematically shown in FIG. 1. The bumper jar 30 is conventionally mounted on a drill string above the junk and cuttings removal tools.

The internal threads 28 may be used for attaching the tool 10 to a boot basket 38 (FIG. 1). The boot basket 38 conventionally carries at its lower end a milling tool 40. Alternatively, the internal threads 22 of the lower sub 20 can be used for attaching the apparatus 10 to a jet sub (not shown) for admitting circulating liquid into the wellbore 34.

Mounted between the subs 16 and 20 are magnet assemblies 24, 26, and 28. The magnet assemblies are vertically spaced from each other and separated by retainer rings 25 and 27. The retainer rings 25, 27 are split rings provided with locking members 29 for securing the magnets on the body 12. The retainer rings 25, 27 also help in retrieving of heavy, shrapnel by creating a “stop,” thereby preventing a sliding and/or flushing effect.

As can be seen in the drawings, magnet assemblies 24, 26, and 28 comprise a plurality of individual magnet members 42. The magnet members 42 have “north” and “south” members FIG. 3), attracting variously charged metal cuttings. Each of the magnet members has a magnet body 44 (FIG. 4) encased in a shielding protector 46. The magnet members 42 may have rectangular cross or a trapezoidal cross-section, or other configuration suitable for securing on the tool body 12.

The protector, or magnet shield 46 has an inner wall 48, an outer wall 50 and side walls 52, 54, 56, and 58. The inner wall 48 has an increased thickness, while the outer wall 50 and side walls 52, 54, 56, and 58 are formed relatively thin as compared to the inner wall 48. The increased thickness of the inner wall 48 and thin outer and side walls facilitate concentrating of the magnetic force outwardly, from the tool body 12 and into the casing annulus.

The shape and size of the magnet shield 46 closely follows the configuration of the magnet body 44. In the preferred embodiment, the magnet shields 46 are formed from a non-ferrous material, which is non-magnetic, but rather allows the magnetic force to penetrate therethrough and attract the metal debris from the well bore.

A portion of each magnet member 42 fits into a specially provided slot, or groove 60 formed in the body 12. The inner wall 48 and small portions of the side walls 52, 54 of the magnet shield 46 fit into the corresponding slot 60. If desired, the outer wall of the magnet body 44 and the shield 46 may be formed arcuate, generally following the outline of the body 12.

When cuttings appear in an annulus 62 of a casing 64 the magnet protectors 46 deflect the striking force of the metal cuttings, protecting the magnet surfaces of the magnet body 44 and cause them to strike the outer wall 50 and the side walls 52, 54, 56 and 58. The cuttings then attach themselves to the magnet members 42 and can be carried to the surface when the tool 10 is retrieved.

It is preferred that the magnet members 42 cover more than one-half of the exterior surface of the tool 10. The magnetic field created by the magnet bodies 44 causes some of the metal debris to be caught between the magnet members 42. The cuttings accumulate within this trap space and are held there until milling is finished and the tool 10 is retrieved.

This procedure is different from conventional methods, where a mule shoe first removes small particles and then cutting or milling is performed. The apparatus of the present invention allows performing several procedures in one step. It is possible to still use a cuttings boot basket, if desired for maximum removal of cuttings, although experiments performed with the apparatus of the present invention demonstrated a significantly high cutting removal rate.

The tool of the present invention is particularly advantageous in horizontal or directional drilling where gravity-assisted cuttings collection is not available. The tool of the present invention, by attracting the cuttings and holding them in “traps” facilitates a greater rate of cuttings removal than was available before.

Although three sets of magnet assemblies 42 are shown in FIG. 2, each consisting of vertically and circumferentially spaced magnet members, it will be understood that the number of the magnet assemblies can be easily modified depending on the design and strength of the magnets. Moreover, more than one tool 10 may be provided on the drill string, if desired, as schematically illustrated in FIG. 1.

The number of individual magnet members 42 in a magnet assembly can vary. Normally, four or five magnets work satisfactorily when equidistantly spaced about the circumference of the body 12. During rotation of the tool 10, the magnets provide an almost 360 degree coverage and create a strong magnetic field for attracting metal cuttings and miscellaneous items.

In conventional operations, the first step is usually to remove sand or small soil particles that accumulated on top of a packer. Using a drill stem to lower a circulating pipe with an angularly cut nozzle to the depth where the packer is located usually performs this step. The circulating air/fluids stream lifts up the sand, mixes it with the drilling mud solution and carries it to the surface. To increase lifting capability, fluids that are more viscous may be used. The present invention also uses high viscous fluids. However, these fluids assist in moving the cuttings into the “traps.”

However, even fluids with high viscosity value are unable to lift up metal cuttings. Therefore, the next conventional step is to use a milling tool that will cut away pieces of metal and allow the circulating fluid to carry them up to the surface. The tool of the present invention can be lowered into a wellbore together with the with a milling bit, as shown in FIG. 1, or a jet, thus eliminating one or even two steps of conventional methods.

By using a magnetic tool together with the milling bit the user effectively introduces the retrieval means directly into the working stream and facilitates immediate adherence of the cuttings to the magnets. Consequently, the time lost in removing the packer can be effectively minimized. The tools 10 of the present invention may be used for any length of time in the well bore. In contrast, a conventional “hydrostatic surge tool” must be retrieved and reset after a four- or five-time surge. It may take from 1 to 5 minutes to complete a surge cycle.

Even further, a “hydrostatic surge tool” can retrieve large pieces of debris but it will not allow recovery of small cuttings and other metal pieces. Since conventional tools do not have circulating capabilities, they often become plugged with cuttings and miscellaneous debris, which prevents proper operation and creates a hazard in the event of a “kick” or “blow-out.” In contrast, the tool of the present invention, by allowing circulation, does not become plugged and will not hinder a well-killing operation.

The size and number of the magnet members 42, as well as the number of magnet assemblies can vary, depending on the size of the drill string, the diameter of the annulus and the amount of cuttings to be retrieved. If desired, the magnets may be staggered or offset from each other in relation to the magnet assemblies to achieve maximum efficiency. The magnet member may be manufactured from ceramic or rare earth material, insulated and/or stainless steel coated to ensure a long service life.

It is envisioned that the tool of the present invention may be designed with magnets positioned on the interior wall of the central opening. The internal positioning will allow for reverse circulating retrieval of larger pieces of debris. The diameter of the tool may be reduced to run with wire-line or coiled tubing, if necessary, although larger scale tools may be produced based on the principles discussed above. The tool of the present invention may be successfully run with casing scrapers, scratchers and/or brush tools when conditioning of the well bore for production equipment takes place.

The profile of the magnets positioned on the tool bodies assures 360-degree coverage with right-hand rotation. The tool will continue to work even when circulation stops and even in high temperature environment. Since the tool has no “skirts” it may be successfully employed in perforated zones without the fear of hang-ups in cased holes or where casing has splintered. The tool connections have conventional sizes to allow connecting of the tool body with currently used drilling and work over equipment. Oversized tool joints create a centralizing effect and allow retrieval of cuttings and debris without being pulled off the tool during retrieval.

The apparatus of the present invention may be successfully used for a number of operations, such as running above reverse circulation baskets to catch miscellaneous pieces, bearings, rings, etc.; for running with fishing magnets to retrieve various items from the wellbore; for running with a mule shoe to wash sand and recover miscellaneous items; for running with milling equipment to recover cuttings from a well bore. The latter type of use has an additional benefit of keeping the cuttings away from the milling bit to allow for more efficient milling operations.

The tool of the present invention may be also used for running below a tubing conveyed perforating guns to recover shrapnel from the well bore, for running with J-latch or conventional overshot to recover miscellaneous items and retrieve packer plugs; for running with a jet sub for stirring miscellaneous debris and retrieving it to the surface, which allows recovery without wedging debris, as it happens when conventional equipment is used. The magnetic tools of the present invention can be also run in tandem in heavy milling and fishing operations. It can be successfully used for retrieval of various small tools and parts dropped accidentally into the well bore.

Due to a streamline design of the apparatus of the present invention, it can be washed over and retrieved with conventional fishing methods, if necessary. Such result cannot be achieved with conventional boot baskets that traditionally have oversized skirts. Removing the retrieved cuttings and cleaning of the tool of the present invention is relatively simple, and the tool can be run down hole again in a matter of minutes.

Many changes and modification can be made in the design of the present invention without departing from the spirit thereof. I, therefore, pray that my rights to the present invention be limited only by the scope of the appended claims. 

1. An apparatus for retrieving metal objects from a wellbore, comprising: a cylindrical tool body with a central opening therethrough; a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of elongated magnet members spaced equidistantly from each other about the circumference of said tool body, each of said magnet members comprising a separate shield protecting at least an outer front wall of a corresponding magnet member.
 2. The apparatus of claim 1, wherein each of said magnet members comprises a magnet body and a shield mounted about said magnet body.
 3. The apparatus of claim 2, wherein said is configured to encase the magnet body.
 4. The apparatus of claim 2, wherein said shield is provided with means for concentrating magnetic force and directing said magnetic force outwardly from the tool body.
 5. The apparatus of claim 2, wherein said shield comprises an inner wall engaging the tool body and an outer wall, and wherein said inner wall has greater thickness than the outer wall.
 6. The apparatus of claim 2, wherein said shield comprises an inner wall contacting the tool body, an outer wall, and a side wall, and wherein said side wall and said outer wall form settling surfaces for the metal objects being attracted by the magnet body.
 7. The apparatus of claim 2, wherein said shield has a configuration complementary to a configuration of a corresponding magnet body.
 8. The apparatus of claim 7, wherein said magnet body and said shield each have a generally trapezoidal cross-section.
 9. The apparatus of claim 1, wherein said tool body is provided with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the well bore.
 10. The apparatus of claim 1, wherein said tool body is provided with a plurality of recesses for receiving an inner wall of a corresponding magnet member therein.
 11. An apparatus for retrieving metal objects from a wellbore, comprising: a cylindrical tool body with a central opening therethrough; a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of elongated magnet members, each of the magnet members comprising a magnet body encased in a non-magnetic shield.
 12. The apparatus of claim 11, wherein said shield has a configuration facilitating concentration of magnetic force outwardly away from the tool body.
 13. The apparatus of claim 12, wherein said shield has an inner wall fitted into a recess formed in the tool body, a side wall and an outer wall, and wherein said inner wall has thickness greater than said side wall and said outer wall.
 14. The apparatus of claim 13, wherein said side wall and said outer wall form a settling surface for the metal objects being attracted by the magnet body.
 15. The apparatus of claim 11, wherein each of said magnet members has a cross section of a generally trapezoidal configuration, and wherein said magnet members are secured longitudinally on the tool body.
 16. An apparatus for retrieving metal objects from a wellbore, comprising: a cylindrical tool body with a central opening therethrough; a plurality of magnet assemblies spaced longitudinally along the length of the tool body and covering a majority of surface area of said tool body, each of said magnet assemblies comprising a plurality of magnet members detachably secured on said tool body, each of said magnet members comprising a magnet body encased in a shield, said shield having configuration complementary to a configuration of a corresponding magnet body.
 17. The apparatus of claim 16, wherein each of said magnet members is fitted into a corresponding recess formed in the tool body.
 18. The apparatus of claim 16, wherein said shield comprises an inner wall, an outer wall and a side wall, and wherein said inner wall has a thickness smaller than the thickness of the outer wall and the side wall to facilitate concentration of magnetic force created by the magnet body away from the tool body.
 19. The apparatus of claim 16, wherein said tool body is provided with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the wellbore.
 20. A method of retrieving metal particles from a well bore, comprising the following steps: providing a tool body having a central opening therein; providing a plurality of magnet assemblies longitudinally spaced along said tool body, each magnet assembly comprising a plurality of magnet members, said magnet members covering a majority surface area of said tool body, each of said magnet members comprising a shield separately encasing individual magnet bodies; detachably non-rotatably securing each of said magnet members on said tool body; and lowering said body into the well bore and imparting rotation to said tool body, thereby creating a magnetic field and causing metal particles to settle on said magnet assemblies.
 21. The method of claim 18, wherein exterior surfaces of said magnet members define metal particles settling area.
 22. The method of claim 18, further comprising a step of forming each of said shields from a non-ferrous material.
 23. The method of claim 18, further comprising a step of forming each of said shields having an inner wall, an outer wall and a side wall, and positioning the inner wall of each of said shields in a corresponding recess formed in the tool body.
 24. The method of claim 21, further comprising a step of forming each of said shields with the inner wall having a thickness greater than thickness of said outer wall and said side wall, thereby concentrating magnetic force away from the tool body and into the well bore.
 25. The method of claim 20, further comprising the step of providing said shield and said magnet body with complementary configurations.
 26. The method of claim 20, further comprising a step of providing said tool body with with an upper sub located above said magnet assemblies and a lower sub located below said magnet assemblies, said upper sub and said lower sub allowing connection of said body to a drill string lowered into the wellbore.
 27. A method of retrieving metal particles from a well bore, comprising the following steps: providing a tool body having a central opening therein; providing a plurality of magnet assemblies longitudinally spaced along said tool body, each magnet assembly comprising a plurality of magnet members, each of said magnet members comprising a shield separately encasing individual magnet bodies for creating individual protecting barrier about entire exterior surface of the magnet body against striking force created by attracted metal particles; detachably securing each of said magnet members on said tool body; lowering said body into the well bore; and imparting rotation to said tool body, thereby creating a magnetic field and causing metal particles to settle on said magnet assemblies.
 28. The method of claim 27, further comprising a step of forming each of said shields with the inner wall having a thickness greater than thickness of said outer wall and said side wall, thereby concentrating magnetic force away from the tool body and into the well bore. 